Abstract
We designed a new system that eliminates deviations by correcting uncertainty in optical distance measurements in the laser two-color heterodyne interferometer. In simulations, eliminating the uncertainty from the atmosphere, the deviation in the uncertainty of the optical distance was 50 times greater with the two-color method than with the one-color method. Adding a correction arm reduces the deviation caused by the uncertainties in measured optical distances. The uncertainty in the measured path length is reduced to 20 nm over a path length of 1500 mm, giving a relative uncertainty of 1.34 × 10−8.
Highlights
Heterodyne laser interferometers are used extensively in stage measurements because they have high resolution, precision, speed, and multiple channels[1,2,3]
We report a combination of the two-color method and the heterodyne laser interferometer, which can improve the resolution by adding an uncertainty correction system for the measured optical distances
A schematic of the two-color heterodyne laser interferometer with a correction of uncertainties in measured optical distances is shown in Fig. 1, both of the two-colored light beams consist of two coherent, collimated, orthogonally polarized frequency components
Summary
Heterodyne laser interferometers are used extensively in stage measurements because they have high resolution, precision, speed, and multiple channels[1,2,3]. The influence of the turbulence of the atmosphere can be corrected using the two-color method proposed by Bender and Owens[9, 10], which is widely used in optical frequency combs[11,12,13,14] and laser interferometers[15,16,17,18] This method measures a geometric distance, L, with both wavelength λ1 and λ2, to obtain two optical distances, Lλ1 and Lλ2, and gives the geometric distance L = Lλ1 − A(Lλ2 − Lλ1), where A is the so-called A-coefficient in two-color method that represents the dispersion relation for air refractive indices at two wavelengths.The conventional two-color method eliminated the influence of the atmosphere, yet simultaneously enlarged the uncertainties in measured optical distances, ΔLλ1 and ΔLλ2, because of the stability of the laser wavelength, thermal expansion and the optical thermal drift[19]. The influence of the atmosphere and the uncertainty in measured optical distances are successfully eliminated and the uncertainty of the measurement of the 1500 mm distance is less than 20 nm
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